A typical bipolar electrolytic cell comprises an outer frame or housing, such as a dielectric plastic, enclosing and supporting a number of bipolar units arranged in series. Each unit comprises parallel anode and cathode plates spaced by a partition or centerboard. In each unit, the centerboard may comprise a form sustaining steel plate confronting and spaced from the cathode plate, and a titanium sheet bonded to the steel plate and confronting and spaced from the anode plate. A low resistance electrical connection between the anode and cathode plates of the unit may include a plurality of copper rods extending through the partition or centerboard and having their opposite ends protected from electrolyte in the cell by means of anode and cathode protective covers electrically connected with the associated ends of the copper rods.
In one conventional cell known as a deNora cell, each copper rod extends in screw threaded relationship through the centerboard. One outer end of the threaded rod projects from the anode surface of the centerboard, i.e. the titanium sheet, and screws into an internally threaded tubular titanium sleeve. An inner end of the sleeve is welded to the titanium sheet to effect a seal entirely around the copper rod. The interior of an outer end portion of the titanium sleeve is welded and bonded electrically to the copper rod by means of a silver filler or suitable alloy for effecting a welded electrical connection between the titanium sleeve and copper rod. The protective anode cover is completed by means of a titanium disc welded to the outer end of the titanium sleeve to close the same and shield the welded bond between the sleeve and rod from electrolyte within the cell.
Similarly, an internally threaded tubular steel sleeve is screwed onto a threaded end of the copper rod that projects from the cathode surface or steel plate of the centerboard. An inner end of the steel sleeve is welded to the steel plate to effect a seal entirely around the copper rod. The interior of an outer end portion of the steel sleeve is welded and bonded to the copper rod by means of a silver filler or suitable electrically conducting alloy, such as mentioned above, and a steel disc is welded to the outer end of the steel sleeve to close the same and complete the protective anode cover for shielding the welded bond between the steel sleeve and copper rod from electrolyte within the cell.
A comparatively large number of the low resistance connections between the parallel anode and cathode plates are required (74 in a typical cell) because the connections also serve to support the plates precisely in parallelism with each other. In consequence, the conventional construction requires a large number of difficult, costly, and time consuming manual welding operations. Furthermore, the electrical connection between the titanium sleeve and copper rod depends in part upon the screw-threaded connection. During operation of the cell, a titanium oxide film gradually develops at the region of the threaded connection, increasing the electrical resistance between the sleeve and rod and gradually impairing the efficiency of the cell which desirably operates at a low potential difference and high current flow between the parallel plates of adjacent units, as for example in the neighborhood of 3 volts and 2 ampers per square inch.
Important objects of the present invention are to provide improvements in bipolar cells of the general type described wherein reliance upon a threaded engagement between a titanium sleeve and copper rod for an electrical connection is avoided, and to provide improvements in the process of manufacturing such a cell whereby the heretofore laborious manual welding between each copper rod and associated anode protective cover is replaced by high speed automated welding procedures that provide a non-corrosive direct surface-to-surface weld between the rod and cover, thereby to materially reduce the time and cost of manufacturing the cell and also to increase its useful operating life by eliminating the heretofore screw threaded electrical connection between each copper rod and associated protective titanium cover.
Other objects are to provide improved means for supporting the anode and cathode plates parallel to each other and for avoiding localized pressure on these plates at the regions of support.
The foregoing objects are accomplished by providing a partition or centerboard having a number of holes spaced over its surface and extending therethrough for a corresponding number of copper rods as required for the electrical connections. At the cathode side of the centerboard, a separate steel sleeve is associated with the cathode end of each copper rod and is provided at one end with a coaxial endwise tapering annular welding projection adapted to seat against the centerboard steel plate entirely around the associated hole through which the copper rod extends. The centerboard is then assembled with the steel sleeves aligned coaxially with their respective holes and with the annular welding projections pressing against the steel plate around the holes. The assembled steel sleeves and steel plate are then welded together under pressure by conventional projection welding procedures. By reason of the annular tapered welding projection of each sleeve, the electrical resistance and consequent heat of the welding operation is concentrated at the tapered extremity of each welding projection to effect a positive weld between the steel plate and each sleeve entirely around the associated centerboard hole.
Each copper rod is dimensioned to pass freely through its associated centerboard hole and coaxially into the associated steel sleeve that is welded to the steel plate at the cathode side. A separate cup shaped or thimble type titanium button is provided with an opening at one end dimensioned to receive the anode end of each copper rod freely. The interior base of the opening is shaped to conform closely to the latter end, which is seated under pressure against the conforming interior base of the opening. The rod and button are then frictionally welded together by conventional friction welding procedure, as for example by relative spinning of the parts while being pressed together, to effect a non-oxidizable electrical connection therebetween. The surface area of the frictionally welded parts is sufficient to achieve the desired low resistance electrical connection therebetween that is not subject to deterioration by oxidation. No additional electrical connection is required, such as a silver or alloy filler used heretofore.
Each titanium button is also provided around the mouth of its opening with an annular endwise tapering welding projection arranged to seat against the titanium sheet entirely around the associated centerboard hole through which the copper rod projects. The centerboard and welded together titanium buttons and copper rods are assembled with the rods passing through their respective centerboard holes and coaxially into the steel sleeves welded to the cathode side of the centerboard, and with the annular welding projections of the titanium buttons pressed against the titanium sheet around their respective centerboard holes. The latter are sufficiently oversize with respect to the copper rods to enable their radial adjustment in the holes to accommodate production deviations from coaxial alignment of the steel sleeves and titanium buttons.
The titanium buttons are projection welded to the titanium sheet by conventional projection welding procedures. The tapered annular welding projections provide the high electrical resistance at the annular region of contact with the titanium sheet to effect a positive weld thereto and seals entirely around the associated copper rods.
In accordance with conventional practice, the interior of each steel sleeve is welded to the cathode end of the associated copper rod by means of a silver filler or suitable welding alloy, including but not limited to aluminum bronze, silicon bronze, nickel and nickel based alloys. The outer end of the steel sleeve remote from the partition wall is then closed by welding a steel cap thereto by conventional procedures, as for example by metal inert gas (MIG) welding, thereby to provide in cooperation with the titanium button at the anode side of the partition wall a complete closure for the copper rod and a low resistance electrical connection from the steel sleeve to the titanium button via the copper rod.
The electrical connection between the parallel anode and cathode plates is preferably completed by electrically connecting only one of the protective covers for each copper rod directly to one of the latter plates. Thus, if the anode cover is connected directly to the anode plate, the cathode cover at the opposite end of the copper rod will not be connected directly to the cathode plate, and vice versa. By way of example in a preferred construction, titanium ribs extend between and are connected in adjusted positions by welding, as described herein, to adjacent titanium anode protective covers. An outer edge of each rib extends in parallelism with the anode plate and is also welded thereto, such that the ribs complete a direct electrical connection between the anode covers and the anode plate, rigidify the cell structure, and maintain the anode plate in a predetermined plane.
Spaced over the surface of the partition or centerboard and also radially from the copper rods that extend through the centerboard are a plurality of steel spacer buttons or members welded in the preferred construction to the steel centerboard plate. Similarly to the titanium ribs, steel ribs extend between and are welded in adjusted positions to adjacent steel spacer buttons. The edges of the steel ribs adjacent to the cathode plate define a surface in parallelism with the anode plate and are welded to the cathode plate to complete an electrical connection between the cathode plate and steel centerboard plate and through the latter to the steel protective covers and copper rods. Likewise, the steel ribs cooperate with the titanium ribs to rigidify the cell structure and maintain the cathode and anode plates of adjacent bipolar units in closely spaced parallelism with each other. By virtue of the steel spacer members or buttons spaced radially from the titanium anode covers, the supports for the anode and cathode plates are not aligned with each other and localized pressure on these plates is avoided, as would otherwise result from a stack-up of dimensional tolerances or thermally induced dimensional changes.
Also in a preferred construction, similarly to the welding projections provided on the protective covers for the ends of the copper rods, prior to welding the steel spacer buttons to the steel centerboard plate, a face of each such button is provided with an annular endwise tapering welding projection to facilitate welding of the spacer buttons to the steel centerboard plate by conventional projection welding procedures.
According to a further improvement described in detail herein, titanium rings are welded at their inner peripheries in adjusted positions around each titanium button. Similarly steel rings are welded at their inner peripheries in adjusted positions around each steel spacer button or member. The titanium ribs extend between the outer peripheries of adjacent titanium rings and are welded thereto. Likewise, the steel ribs extend between and are welded to the outer peripheries of adjacent steel rings that extend around the steel spacer members. The ends of the steel ribs welded to the steel rings and the ends of the titanium ribs welded to the titanium rings are tapered endwise to facilitate welding of these ribs to their respective rings by conventional projection welding. Costly and laborious titanium inert gas (TIG) or metal inert gas (MIG) welding that have been conventional heretofore are thus avoided.
Furthermore, by virtue of the titanium and steel ribs welded to their respective rings, these elements may be suitably supported in welding jigs and adjusted prior to the welding operations until the outer edges of the ribs that are or will be subsequently welded to the anode and cathode plates define predetermined planes. The inner peripheries of the rings are sufficiently oversize with respect to the parts to which they are welded such that prior to the welding they may be adjusted axially and radially with respect to the latter parts to accommodate production tolerances in the welding of the ribs to the outer peripheries of the rings and to assure both the proper spacing between the anode and cathode plates as well as their parallelism in the completed electrolyte cell.
Other objects of this inventions will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.